Abstract: The acoustic emission technique was employed for the monitoring of couplet box tube socket weld injury changes in the boiler hydrostatic test process. By finding damage activity signals in the complex interference noise background and by the analysis of the mechanism of injury-induced acoustic emission characterization, the signals characteristic of weld cracks were obtained. The combination of real-time monitoring methods using acoustic emission and offline ultrasonic detection methods has resulted in a comprehensive evaluation of couplet box header internal damage location and damage development during hydrostatic testing process. The combination of the two methods, as well as the mutual authentication can improve the reliability, which plays an important role in guiding the on-site testing.